1 /*

     2  * Copyright 1998-2006 Sun Microsystems, Inc.  All Rights Reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.  Sun designates this

     8  * particular file as subject to the "Classpath" exception as provided

     9  * by Sun in the LICENSE file that accompanied this code.

    10  *

    11  * This code is distributed in the hope that it will be useful, but WITHOUT

    12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    14  * version 2 for more details (a copy is included in the LICENSE file that

    15  * accompanied this code).

    16  *

    17  * You should have received a copy of the GNU General Public License version

    18  * 2 along with this work; if not, write to the Free Software Foundation,

    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

    21  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

    22  * CA 95054 USA or visit www.sun.com if you need additional information or

    23  * have any questions.

    24  */

    25 

    26 package java.util;

    27 

    28 /**

    29  * A {@link NavigableSet} implementation based on a {@link TreeMap}.

    30  * The elements are ordered using their {@linkplain Comparable natural

    31  * ordering}, or by a {@link Comparator} provided at set creation

    32  * time, depending on which constructor is used.

    33  *

    34  * <p>This implementation provides guaranteed log(n) time cost for the basic

    35  * operations ({@code add}, {@code remove} and {@code contains}).

    36  *

    37  * <p>Note that the ordering maintained by a set (whether or not an explicit

    38  * comparator is provided) must be <i>consistent with equals</i> if it is to

    39  * correctly implement the {@code Set} interface.  (See {@code Comparable}

    40  * or {@code Comparator} for a precise definition of <i>consistent with

    41  * equals</i>.)  This is so because the {@code Set} interface is defined in

    42  * terms of the {@code equals} operation, but a {@code TreeSet} instance

    43  * performs all element comparisons using its {@code compareTo} (or

    44  * {@code compare}) method, so two elements that are deemed equal by this method

    45  * are, from the standpoint of the set, equal.  The behavior of a set

    46  * <i>is</i> well-defined even if its ordering is inconsistent with equals; it

    47  * just fails to obey the general contract of the {@code Set} interface.

    48  *

    49  * <p><strong>Note that this implementation is not synchronized.</strong>

    50  * If multiple threads access a tree set concurrently, and at least one

    51  * of the threads modifies the set, it <i>must</i> be synchronized

    52  * externally.  This is typically accomplished by synchronizing on some

    53  * object that naturally encapsulates the set.

    54  * If no such object exists, the set should be "wrapped" using the

    55  * {@link Collections#synchronizedSortedSet Collections.synchronizedSortedSet}

    56  * method.  This is best done at creation time, to prevent accidental

    57  * unsynchronized access to the set: <pre>

    58  *   SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));</pre>

    59  *

    60  * <p>The iterators returned by this class's {@code iterator} method are

    61  * <i>fail-fast</i>: if the set is modified at any time after the iterator is

    62  * created, in any way except through the iterator's own {@code remove}

    63  * method, the iterator will throw a {@link ConcurrentModificationException}.

    64  * Thus, in the face of concurrent modification, the iterator fails quickly

    65  * and cleanly, rather than risking arbitrary, non-deterministic behavior at

    66  * an undetermined time in the future.

    67  *

    68  * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed

    69  * as it is, generally speaking, impossible to make any hard guarantees in the

    70  * presence of unsynchronized concurrent modification.  Fail-fast iterators

    71  * throw {@code ConcurrentModificationException} on a best-effort basis.

    72  * Therefore, it would be wrong to write a program that depended on this

    73  * exception for its correctness:   <i>the fail-fast behavior of iterators

    74  * should be used only to detect bugs.</i>

    75  *

    76  * <p>This class is a member of the

    77  * <a href="{@docRoot}/../technotes/guides/collections/index.html">

    78  * Java Collections Framework</a>.

    79  *

    80  * @param <E> the type of elements maintained by this set

    81  *

    82  * @author  Josh Bloch

    83  * @see     Collection

    84  * @see     Set

    85  * @see     HashSet

    86  * @see     Comparable

    87  * @see     Comparator

    88  * @see     TreeMap

    89  * @since   1.2

    90  */

    91 

    92 public class TreeSet<E> extends AbstractSet<E>

    93     implements NavigableSet<E>, Cloneable, java.io.Serializable

    94 {

    95     /**

    96      * The backing map.

    97      */

    98     private transient NavigableMap<E,Object> m;

    99 

   100     // Dummy value to associate with an Object in the backing Map

   101     private static final Object PRESENT = new Object();

   102 

   103     /**

   104      * Constructs a set backed by the specified navigable map.

   105      */

   106     TreeSet(NavigableMap<E,Object> m) {

   107         this.m = m;

   108     }

   109 

   110     /**

   111      * Constructs a new, empty tree set, sorted according to the

   112      * natural ordering of its elements.  All elements inserted into

   113      * the set must implement the {@link Comparable} interface.

   114      * Furthermore, all such elements must be <i>mutually

   115      * comparable</i>: {@code e1.compareTo(e2)} must not throw a

   116      * {@code ClassCastException} for any elements {@code e1} and

   117      * {@code e2} in the set.  If the user attempts to add an element

   118      * to the set that violates this constraint (for example, the user

   119      * attempts to add a string element to a set whose elements are

   120      * integers), the {@code add} call will throw a

   121      * {@code ClassCastException}.

   122      */

   123     public TreeSet() {

   124         this(new TreeMap<E,Object>());

   125     }

   126 

   127     /**

   128      * Constructs a new, empty tree set, sorted according to the specified

   129      * comparator.  All elements inserted into the set must be <i>mutually

   130      * comparable</i> by the specified comparator: {@code comparator.compare(e1,

   131      * e2)} must not throw a {@code ClassCastException} for any elements

   132      * {@code e1} and {@code e2} in the set.  If the user attempts to add

   133      * an element to the set that violates this constraint, the

   134      * {@code add} call will throw a {@code ClassCastException}.

   135      *

   136      * @param comparator the comparator that will be used to order this set.

   137      *        If {@code null}, the {@linkplain Comparable natural

   138      *        ordering} of the elements will be used.

   139      */

   140     public TreeSet(Comparator<? super E> comparator) {

   141         this(new TreeMap<E,Object>(comparator));

   142     }

   143 

   144     /**

   145      * Constructs a new tree set containing the elements in the specified

   146      * collection, sorted according to the <i>natural ordering</i> of its

   147      * elements.  All elements inserted into the set must implement the

   148      * {@link Comparable} interface.  Furthermore, all such elements must be

   149      * <i>mutually comparable</i>: {@code e1.compareTo(e2)} must not throw a

   150      * {@code ClassCastException} for any elements {@code e1} and

   151      * {@code e2} in the set.

   152      *

   153      * @param c collection whose elements will comprise the new set

   154      * @throws ClassCastException if the elements in {@code c} are

   155      *         not {@link Comparable}, or are not mutually comparable

   156      * @throws NullPointerException if the specified collection is null

   157      */

   158     public TreeSet(Collection<? extends E> c) {

   159         this();

   160         addAll(c);

   161     }

   162 

   163     /**

   164      * Constructs a new tree set containing the same elements and

   165      * using the same ordering as the specified sorted set.

   166      *

   167      * @param s sorted set whose elements will comprise the new set

   168      * @throws NullPointerException if the specified sorted set is null

   169      */

   170     public TreeSet(SortedSet<E> s) {

   171         this(s.comparator());

   172         addAll(s);

   173     }

   174 

   175     /**

   176      * Returns an iterator over the elements in this set in ascending order.

   177      *

   178      * @return an iterator over the elements in this set in ascending order

   179      */

   180     public Iterator<E> iterator() {

   181         return m.navigableKeySet().iterator();

   182     }

   183 

   184     /**

   185      * Returns an iterator over the elements in this set in descending order.

   186      *

   187      * @return an iterator over the elements in this set in descending order

   188      * @since 1.6

   189      */

   190     public Iterator<E> descendingIterator() {

   191         return m.descendingKeySet().iterator();

   192     }

   193 

   194     /**

   195      * @since 1.6

   196      */

   197     public NavigableSet<E> descendingSet() {

   198         return new TreeSet(m.descendingMap());

   199     }

   200 

   201     /**

   202      * Returns the number of elements in this set (its cardinality).

   203      *

   204      * @return the number of elements in this set (its cardinality)

   205      */

   206     public int size() {

   207         return m.size();

   208     }

   209 

   210     /**

   211      * Returns {@code true} if this set contains no elements.

   212      *

   213      * @return {@code true} if this set contains no elements

   214      */

   215     public boolean isEmpty() {

   216         return m.isEmpty();

   217     }

   218 

   219     /**

   220      * Returns {@code true} if this set contains the specified element.

   221      * More formally, returns {@code true} if and only if this set

   222      * contains an element {@code e} such that

   223      * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.

   224      *

   225      * @param o object to be checked for containment in this set

   226      * @return {@code true} if this set contains the specified element

   227      * @throws ClassCastException if the specified object cannot be compared

   228      *         with the elements currently in the set

   229      * @throws NullPointerException if the specified element is null

   230      *         and this set uses natural ordering, or its comparator

   231      *         does not permit null elements

   232      */

   233     public boolean contains(Object o) {

   234         return m.containsKey(o);

   235     }

   236 

   237     /**

   238      * Adds the specified element to this set if it is not already present.

   239      * More formally, adds the specified element {@code e} to this set if

   240      * the set contains no element {@code e2} such that

   241      * <tt>(e==null&nbsp;?&nbsp;e2==null&nbsp;:&nbsp;e.equals(e2))</tt>.

   242      * If this set already contains the element, the call leaves the set

   243      * unchanged and returns {@code false}.

   244      *

   245      * @param e element to be added to this set

   246      * @return {@code true} if this set did not already contain the specified

   247      *         element

   248      * @throws ClassCastException if the specified object cannot be compared

   249      *         with the elements currently in this set

   250      * @throws NullPointerException if the specified element is null

   251      *         and this set uses natural ordering, or its comparator

   252      *         does not permit null elements

   253      */

   254     public boolean add(E e) {

   255         return m.put(e, PRESENT)==null;

   256     }

   257 

   258     /**

   259      * Removes the specified element from this set if it is present.

   260      * More formally, removes an element {@code e} such that

   261      * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>,

   262      * if this set contains such an element.  Returns {@code true} if

   263      * this set contained the element (or equivalently, if this set

   264      * changed as a result of the call).  (This set will not contain the

   265      * element once the call returns.)

   266      *

   267      * @param o object to be removed from this set, if present

   268      * @return {@code true} if this set contained the specified element

   269      * @throws ClassCastException if the specified object cannot be compared

   270      *         with the elements currently in this set

   271      * @throws NullPointerException if the specified element is null

   272      *         and this set uses natural ordering, or its comparator

   273      *         does not permit null elements

   274      */

   275     public boolean remove(Object o) {

   276         return m.remove(o)==PRESENT;

   277     }

   278 

   279     /**

   280      * Removes all of the elements from this set.

   281      * The set will be empty after this call returns.

   282      */

   283     public void clear() {

   284         m.clear();

   285     }

   286 

   287     /**

   288      * Adds all of the elements in the specified collection to this set.

   289      *

   290      * @param c collection containing elements to be added to this set

   291      * @return {@code true} if this set changed as a result of the call

   292      * @throws ClassCastException if the elements provided cannot be compared

   293      *         with the elements currently in the set

   294      * @throws NullPointerException if the specified collection is null or

   295      *         if any element is null and this set uses natural ordering, or

   296      *         its comparator does not permit null elements

   297      */

   298     public  boolean addAll(Collection<? extends E> c) {

   299         // Use linear-time version if applicable

   300         if (m.size()==0 && c.size() > 0 &&

   301             c instanceof SortedSet &&

   302             m instanceof TreeMap) {

   303             SortedSet<? extends E> set = (SortedSet<? extends E>) c;

   304             TreeMap<E,Object> map = (TreeMap<E, Object>) m;

   305             Comparator<? super E> cc = (Comparator<? super E>) set.comparator();

   306             Comparator<? super E> mc = map.comparator();

   307             if (cc==mc || (cc != null && cc.equals(mc))) {

   308                 map.addAllForTreeSet(set, PRESENT);

   309                 return true;

   310             }

   311         }

   312         return super.addAll(c);

   313     }

   314 

   315     /**

   316      * @throws ClassCastException {@inheritDoc}

   317      * @throws NullPointerException if {@code fromElement} or {@code toElement}

   318      *         is null and this set uses natural ordering, or its comparator

   319      *         does not permit null elements

   320      * @throws IllegalArgumentException {@inheritDoc}

   321      * @since 1.6

   322      */

   323     public NavigableSet<E> subSet(E fromElement, boolean fromInclusive,

   324                                   E toElement,   boolean toInclusive) {

   325         return new TreeSet<E>(m.subMap(fromElement, fromInclusive,

   326                                        toElement,   toInclusive));

   327     }

   328 

   329     /**

   330      * @throws ClassCastException {@inheritDoc}

   331      * @throws NullPointerException if {@code toElement} is null and

   332      *         this set uses natural ordering, or its comparator does

   333      *         not permit null elements

   334      * @throws IllegalArgumentException {@inheritDoc}

   335      * @since 1.6

   336      */

   337     public NavigableSet<E> headSet(E toElement, boolean inclusive) {

   338         return new TreeSet<E>(m.headMap(toElement, inclusive));

   339     }

   340 

   341     /**

   342      * @throws ClassCastException {@inheritDoc}

   343      * @throws NullPointerException if {@code fromElement} is null and

   344      *         this set uses natural ordering, or its comparator does

   345      *         not permit null elements

   346      * @throws IllegalArgumentException {@inheritDoc}

   347      * @since 1.6

   348      */

   349     public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {

   350         return new TreeSet<E>(m.tailMap(fromElement, inclusive));

   351     }

   352 

   353     /**

   354      * @throws ClassCastException {@inheritDoc}

   355      * @throws NullPointerException if {@code fromElement} or

   356      *         {@code toElement} is null and this set uses natural ordering,

   357      *         or its comparator does not permit null elements

   358      * @throws IllegalArgumentException {@inheritDoc}

   359      */

   360     public SortedSet<E> subSet(E fromElement, E toElement) {

   361         return subSet(fromElement, true, toElement, false);

   362     }

   363 

   364     /**

   365      * @throws ClassCastException {@inheritDoc}

   366      * @throws NullPointerException if {@code toElement} is null

   367      *         and this set uses natural ordering, or its comparator does

   368      *         not permit null elements

   369      * @throws IllegalArgumentException {@inheritDoc}

   370      */

   371     public SortedSet<E> headSet(E toElement) {

   372         return headSet(toElement, false);

   373     }

   374 

   375     /**

   376      * @throws ClassCastException {@inheritDoc}

   377      * @throws NullPointerException if {@code fromElement} is null

   378      *         and this set uses natural ordering, or its comparator does

   379      *         not permit null elements

   380      * @throws IllegalArgumentException {@inheritDoc}

   381      */

   382     public SortedSet<E> tailSet(E fromElement) {

   383         return tailSet(fromElement, true);

   384     }

   385 

   386     public Comparator<? super E> comparator() {

   387         return m.comparator();

   388     }

   389 

   390     /**

   391      * @throws NoSuchElementException {@inheritDoc}

   392      */

   393     public E first() {

   394         return m.firstKey();

   395     }

   396 

   397     /**

   398      * @throws NoSuchElementException {@inheritDoc}

   399      */

   400     public E last() {

   401         return m.lastKey();

   402     }

   403 

   404     // NavigableSet API methods

   405 

   406     /**

   407      * @throws ClassCastException {@inheritDoc}

   408      * @throws NullPointerException if the specified element is null

   409      *         and this set uses natural ordering, or its comparator

   410      *         does not permit null elements

   411      * @since 1.6

   412      */

   413     public E lower(E e) {

   414         return m.lowerKey(e);

   415     }

   416 

   417     /**

   418      * @throws ClassCastException {@inheritDoc}

   419      * @throws NullPointerException if the specified element is null

   420      *         and this set uses natural ordering, or its comparator

   421      *         does not permit null elements

   422      * @since 1.6

   423      */

   424     public E floor(E e) {

   425         return m.floorKey(e);

   426     }

   427 

   428     /**

   429      * @throws ClassCastException {@inheritDoc}

   430      * @throws NullPointerException if the specified element is null

   431      *         and this set uses natural ordering, or its comparator

   432      *         does not permit null elements

   433      * @since 1.6

   434      */

   435     public E ceiling(E e) {

   436         return m.ceilingKey(e);

   437     }

   438 

   439     /**

   440      * @throws ClassCastException {@inheritDoc}

   441      * @throws NullPointerException if the specified element is null

   442      *         and this set uses natural ordering, or its comparator

   443      *         does not permit null elements

   444      * @since 1.6

   445      */

   446     public E higher(E e) {

   447         return m.higherKey(e);

   448     }

   449 

   450     /**

   451      * @since 1.6

   452      */

   453     public E pollFirst() {

   454         Map.Entry<E,?> e = m.pollFirstEntry();

   455         return (e == null)? null : e.getKey();

   456     }

   457 

   458     /**

   459      * @since 1.6

   460      */

   461     public E pollLast() {

   462         Map.Entry<E,?> e = m.pollLastEntry();

   463         return (e == null)? null : e.getKey();

   464     }

   465 

   466     /**

   467      * Returns a shallow copy of this {@code TreeSet} instance. (The elements

   468      * themselves are not cloned.)

   469      *

   470      * @return a shallow copy of this set

   471      */

   472     public Object clone() {

   473         TreeSet<E> clone = null;

   474         try {

   475             clone = (TreeSet<E>) super.clone();

   476         } catch (CloneNotSupportedException e) {

   477             throw new InternalError();

   478         }

   479 

   480         clone.m = new TreeMap<E,Object>(m);

   481         return clone;

   482     }

   483 

   484     /**

   485      * Save the state of the {@code TreeSet} instance to a stream (that is,

   486      * serialize it).

   487      *

   488      * @serialData Emits the comparator used to order this set, or

   489      *             {@code null} if it obeys its elements' natural ordering

   490      *             (Object), followed by the size of the set (the number of

   491      *             elements it contains) (int), followed by all of its

   492      *             elements (each an Object) in order (as determined by the

   493      *             set's Comparator, or by the elements' natural ordering if

   494      *             the set has no Comparator).

   495      */

   496     private void writeObject(java.io.ObjectOutputStream s)

   497         throws java.io.IOException {

   498         // Write out any hidden stuff

   499         s.defaultWriteObject();

   500 

   501         // Write out Comparator

   502         s.writeObject(m.comparator());

   503 

   504         // Write out size

   505         s.writeInt(m.size());

   506 

   507         // Write out all elements in the proper order.

   508         for (Iterator i=m.keySet().iterator(); i.hasNext(); )

   509             s.writeObject(i.next());

   510     }

   511 

   512     /**

   513      * Reconstitute the {@code TreeSet} instance from a stream (that is,

   514      * deserialize it).

   515      */

   516     private void readObject(java.io.ObjectInputStream s)

   517         throws java.io.IOException, ClassNotFoundException {

   518         // Read in any hidden stuff

   519         s.defaultReadObject();

   520 

   521         // Read in Comparator

   522         Comparator<? super E> c = (Comparator<? super E>) s.readObject();

   523 

   524         // Create backing TreeMap

   525         TreeMap<E,Object> tm;

   526         if (c==null)

   527             tm = new TreeMap<E,Object>();

   528         else

   529             tm = new TreeMap<E,Object>(c);

   530         m = tm;

   531 

   532         // Read in size

   533         int size = s.readInt();

   534 

   535         tm.readTreeSet(size, s, PRESENT);

   536     }

   537 

   538     private static final long serialVersionUID = -2479143000061671589L;

   539 }